European Patent No. 2 066 996 describes a positioning device in a gantry-type construction in which a cross bar is movably supported between two parallel linear guides, a functional element being movably supported on the cross bar with the aid of a further linear guide, so that this functional element is able to be positioned freely in one plane between the two parallel linear guides. For example, a gripper of an automatic pick-and-place machine, a laser of a laser machining center, or perhaps a probe system of a coordinate measuring machine are possible as the functional element. European Patent No. 2 066 996 deals primarily with the most precise position measurement possible in connection with such positioning devices, since precise positioning of the functional element is often very important.
German Published Patent Application No. 10 2009 008 900 describes such positioning devices in gantry-type construction, as well. For various reasons, they are not easy to control from the standpoint of automatic control engineering. Therefore, a device is described for controlling a positioning device automatically, which permits particularly precise positioning.
If the functional element, which is guided on the cross bar and positioned above the workpiece, must exert considerable force on the workpiece, this may lead to deformation of the components of the positioning device. Because of the great leverage which comes about due to the gantry-type construction, small deformations may already lead to a considerable displacement of the point of application of the tool on the workpiece, which is unacceptable for practical applications with a high requirement for positioning accuracy. An example for such an application is thermocompression bonding, in which electronic components are joined to a printed circuit board by pressure and temperature. Forces up to 500 N may be necessary for this purpose. On the other hand, positioning accuracies in the range of one micrometer and less required in such and comparable applications are not uncommon.
Such great forces are especially problematic when the substrate on which electronic components is placed is not aligned very precisely horizontally, so that the vertical process force is not exerted exactly perpendicularly onto the substrate. The lateral forces thereby resulting are already no longer acceptable in the case of small tiltings of the substrate. In addition, the electronic component to be placed must also be parallel to the printed-circuit-board substrate, which is no longer ensured if the substrate is tilted.
Multicomponent force sensors for measuring axial and lateral forces that may appear in connection with a tool with axial preferential direction are described, for example, in European Patent No. 2 052 810, European Patent No. 0 594 534, and Japanese Patent Application Publication No. S61-28835.